This is the second part of a story told to me by a Carbon atom in my brain. It started with her tale of how she ended up on earth. 

From Wikipedia

You know those places where young humans go and sit by the water in the sun? There’s a lot of ‘chemistry’ goes on, am I right? 1. It’s the same for us atoms – water and sunshine makes for some wild times.

You humans are used to water – you’re practically made of the stuff – but for us it’s really really weird. Water is a whole gang of Oxygen atoms, each with a pair of cute Hydrogens like bunny ears on top and they’ve got this weird thing going on, where they stick to each other, but not too much. If I’m bonded with the right atoms I can just get stuck into the mix. It’s like a great big party in there. You float around and make bonds with whoever else is floating around.

Sunlight makes things happen too, which is where life comes in. I’m a big fan of you living things – as a carbon I feel kind of responsible. There wasn’t much of you lot around to start with, just after I landed on this place, I mean2. I spent a lot of time floating around with a couple of oxygen atoms in the air, carbon dioxide you call it. There wasn’t any Oxygen in the atmosphere then, mostly Nitrogen and some other things. Nitrogen annoys me though. On their own they get up to all sorts of things – you’d be lost without them – but in the air they pair up and just ignore everyone else. You know restaurants on Valentine’s Day, each couple in their own little world? Well that’s the atmosphere is like with Nitrogen around.

I remember how things started getting more interesting. As carbon dioxide I got drawn into this really complicated place, quite green, with lots of complex molecules packed into a bag of water. I soon found myself bound up with lots of other carbons. Sunlight was involved somehow and one of the Oxygen atoms I came in with got kicked out3.  Inside you living things there are these big molecules that make me do things – enzymes you call them. I might be thinking about maybe bonding with this or that atom, when somehow they trip me up and I end choosing the one they want. Every time it happens. I really don’t know how they do it4.

Soon a pattern started to form. I’d get stuck in a big molecule, then eventually turned back into carbon dioxide, float around the air or water for a bit and then get sucked back in again. Take the current loop I’m in, for instance.

A while back I got sucked into a green place in the usual fashion. There was an odd stage when everything got mashed up in water and I ended up in a molecule like the first one I was ever in5. I entered you this way and floated around in some huge sack for a while. I was quite surprised just how much of this molecule there was in there6. Then the enzymes got going and I ended up here in your brain as part of a different carbon molecule. Soon you’re going to take this molecule, mix it with Oxygen and break it up. You get energy to think with, I get turned into Carbon dioxide again and end up back in the air.

So for a long time now, I’ve regularly cycling through these different places – water, air, life and around again. Since that first time things have changed so much around here – the air’s full of Oxygen and these green places get everywhere.

Each cycle is different – sometimes I get to go underground. This can last for a very long time. Usually it’s when I’m in a big carbon molecule that gets buried under sand or mud, deeper and deeper. I’ve always made it back up to the surface though, in the end, to go back round the cycle again. There was one time which was very special though. It really *changed* me.

We’ll save that story for next time